Numerical analysis of the production behaviors and geomechanical responses during natural gas hydrate production by vertical wells fracturing

Trial extraction of natural gas hydrates has made great progress, but the available capacity is still orders of magnitude away from commercial development. Reservoir modification measures are a potential approach to achieve commercial recovery, and previous studies have demonstrated the feasibility of fracturing modification in hydrate reservoirs. The laboratory experimental research on hydrate production by vertical well fracturing combined with depressurization method has been carried out to prove the effectiveness of improving capacity. The presence of fractures enhances conductivity near the wellbore, thereby facilitating the propagation of pressure drops and augmenting thermal energy transfer. Whereas hydrate decomposition causes a reduction in reservoir strength and stiffness, potentially resulting in formation subsidence, wellbore failure, and other catastrophic events. Therefore, it is important to understand the geomechanical response for designing fracturing modifications in hydrate reservoirs. As a continuation of previous research, we constructed a coupled model of thermal-hydro-mechanical to investigate the production characteristics and geomechanical response patterns during vertical well fracturing combined with depressurization method to extract hydrates. The results show that fracturing modification helps to shorten the duration of “self-locking effect” and improve the gas-water ratio of gas hydrate extraction. Fractures induces the stress concentration near the wellbore, exacerbating both the subsidence and uplift of caprocks. Under the condition of controlled geological risk, priority should be given to extracting reservoirs with high saturation and high original permeability.